1. Field of the Invention
This invention relates to coated paperboards which, when converted to containers, can be used in microwave applications without emitting unacceptable amounts of benzene. Particularly, this invention relates to containers including a microwave interactive layer wherein at a microwave cooking temperature of about 430.degree. F. or more, less than 0.1 milligrams of benzene are evolved per square inch of the container surface.
2. Background
Disposable paper containers, such as plates, trays, bowls, airline meal containers and cafeteria containers, are commonly produced by pressing flat paperboard blanks into the desired shape between appropriately shaped and heated forming dies. Various protective coatings are typically applied to the blanks before forming to make the resulting paperboard containers moisture-resistant, grease-resistant, more readily printable, etc. Often, printing is also applied to the top surface for decoration. Large numbers of paper products are produced by this method each year. These products come in many different shapes and sizes, including round, rectangular, and polygonal.
When a container is made by pressing a flat paperboard blank, the blank must contain enough moisture to make the cellulosic fibers in the blank sufficiently plastic to permit it to be formed into the desired three-dimensional container shape. During the pressing operation, most of this moisture escapes from the uncoated bottom surface of the blank as water vapor. Suitable methods of producing paperboard containers from moistened paperboard blanks are generally described in U.S. Pat. Nos. 4,721,499 and 4,721,500, among others.
Many people prefer disposable containers which, when handled, produce a sense of bulkiness and grippability at least suggestive of the more substantial non-disposable containers which they replace. While a sense of bulkiness may be provided to some extent in styrofoam and thick pulp-molded containers, such containers suffer a number of drawbacks and cannot include a microwave interactive layer. For example, unlike pressed paperboard containers, styrofoam containers are often brittle and they are environmentally unfriendly because they are not biodegradable and melt under microwaved conditions. Also, styrofoam containers are not cut-resistant and it is difficult to apply printing to the surface of styrofoam containers. Additionally, because of their bulkiness, styrofoam containers take up large amounts of shelf space and are costly to ship. Pulp-molded containers similarly are not cut-resistant and have poor printability characteristics. Additionally, pulp-molded containers typically have weak bottoms. Pressed paperboard containers, however, are cut-resistant, readily printable, strong in all areas, and are far less bully than styrofoam or pulp-molded containers and can include a microwave interactive layer.
The prior art paperboard containers have difficulty in meeting the new low benzene evolution standards set by the food processors and therefore cannot safely be used in microwave applications or include a microwave interactive layer since their coatings emit an unacceptable amount of benzene. Benzene is a well known carcinogen and its contact with food should be minimal.